Video discs are manufactured by producing a "master" with the video information recorded in surface relief, and using the master to press, or mold, mirror images of the relief into a suitable substrate. In one method conventionally used to produce a master, a thin film of a material having a low melting point and low thermal conductivity, such as bismuth, tellurium or tellurium-based media, is applied to a suitable substrate, such as glass and selected, localized portions of the film are then ablated to form pits which have a sequential correspondence to the video data. A series of other operations are then performed in order to provide a mirror image of the sequence of pits, that is, a sequence of bumps or protrusions which provide the surface relief. Once attained, the master is used in a press or injection molding apparatus to obtain on a plastic disc mirror image copies of the surface relief.
For several reasons, it would be highly advantageous to be able to form the surface relief directly; i.e., without initial formation of a sequence of ablated pits. For example, a directly formed master would be less expensive to manufacture and could utilize materials less costly than tellurium, the ablation process results in vaporization debris which may provide a lower than desired signal-to-noise ratio, and tellurium has toxicity concerns.